IT is day 18 of the trial of former Brookfield real estate agent Gerard Baden-Clay, 43, who stands accused of murdering his wife Allison Baden-Clay, 43, on April 19, 2012.

Baden-Clay has pleaded not guilty in the Supreme Court in Brisbane.

Brisbane Supreme Court Justice John Byrne has asked a jury to retire to consider a verdict in the trial of Gerard Baden-Clay.

He asked the jury to retire at 11.10am.

Justice Byrne discharged three reserve jurors who had patiently listened to evidence over the past month.

He thanked them for their service.

Justice Byrne first summarised the defence case for the jury.

He said barrister Michael Byrne QC, for the accused, told the jury in his closing address that family, friends and the Baden-Clay children had never seen them argue or be violent.

He said Mr Byrne told them that even when confronted with an angry mistress in Toni McHugh, he did not grow violent.

Justice Byrne said Mr Byrne told the jury it should find his client did not kill his wife.

He said Mr Byrne told the jury not to speculate and to use evidence to support any inference they would draw.

He said Mr Byrne told the jury no blood was found in the house.

Mr Byrne asked the jury how the accused killed his wife on the prosecution case, Justice Byrne said.

He said that forensic pathologist Dr Nathan Milne was unable to establish a cause of death and there were few injuries on the body.

He said Dr Milne could not say whether a possible bruise in the ribs was caused before or after death.

He said Mr Byrne told the jury the pathologist was unable to exclude drowning, toxicity or falling from a height into water as possible causes of death.

Justice Byrne said Mr Byrne submitted there was no discernable cause of death.

He took the jury to features of the police investigation.

Justice Byrne said Mr Byrne told the jury Baden-Clay gave consent for police to examine the house, look at the cars and around the house.

Mr Byrne, he said, told the jury a crime scene warrant was taken out on the Baden-Clay house at Brookfield.

He said Sen-Sgt Ewen Taylor found no blood or obvious signs of a clean-up inside the home.

He said Mr Byrne told the jury none of the Baden-Clay children heard a fight between their parents, nor car noises on the night of April 19, 2012.

He said Mr Byrne argued Ms Baden-Clay was wearing pyjamas on the night of April 19, 2012, consistent with evidence from one of the children, but was found wearing her walking clothes.

He argued a blood stain found in the Holden Captiva could not be aged and was mistaken for spilled soft drink.

Justice Byrne said Mr Byrne told the jury that on the prosecution case, the accused stopped the car near the bridge and managed to get the body through the grass, drove home and parked it in the car port.

He said Mr Byrne asked the jury whether such a scenario was possible.

He said Mr Byrne submitted an absence of mud in the car was significant.

Justice Byrne said Mr Byrne argued his client had no intention of leaving his wife for Ms McHugh and it was not likely he killed his wife to be with her.

He said Mr Byrne told the jury that when the accused confessed to the affair with his wife there were no raised voices.

He said Mr Byrne told the jury they should reject a premeditated killing or a sudden explosion of temper on the night of April 19, 2012.

He said Mr Byrne argued there was no evidence his client had a violent temper.

Justice Byrne said Mr Byrne told the jury it was "ridiculous" he would murder his wife over financial pressures.

He said Mr Byrne told the jury the position of the body was below the high water mark.

He said Mr Byrne told the jury Baden-Clay never sought to conceal the marks on his face other than to say they were shaving cuts, caused by using an old razor in a hurry.

Justice Byrne said Mr Byrne argued that while experts who assessed the injuries thought they were consistent with fingernail scratches, they could not be certain the marks were not caused by a razor.

He told the jury Mr Byrne said Ms Baden-Clay was first treated by psychiatrist Dr Tom George in 2003 and had symptoms of low mood, anxiety and teary.

He said Mr Byrne argued the deceased was experiencing the same symptoms when visiting her GP in 2011.

He said Mr Byrne took the jury to the evidence of Dr Michael Schramm and psychologist Rosamund Nutting.

He said Mr Byrne argued symptoms of her past depression were recurring and there was a "high chance" she was relapsing in her depressive illness.

He said Mr Byrne told the jury that on April 18, 2012 the accused and his wife had a question and answer session about the affair at Mt Coot-tha, then returned home to news that Baden-Clay's brother had a new baby boy.

He said Mr Byrne asked the jury to consider whether the deceased had always wanted a son and whether the new baby's birth lead to her increasing her medication on the morning of April 19, 2012.

Justice Byrne said Mr Byrne told the jury that after Ms Baden-Clay returned home that night, they revisited questions asked at Mt Coot-tha the night before, and she stayed up, thinking about the affair when the "rawness opened up".

He said Mr Byrne asked the jury whether it was possible Ms Baden-Clay took a tablet and went for a walk, perhaps in disorientation, and by 4am, hallucinated and "ended up in the creek".

He said Mr Byrne told the jury Baden-Clay had no reason and no apparent means to kill his wife.

Justice Byrne said Mr Byrne told the jury his client told Ms McHugh to tell police the truth, contrary to the conduct of someone who had just killed his wife.

He said Mr Byrne contended that once you assessed the whole of the evidence you would not convict his client.